Mixing device for mixing fuel and air and furnace with a mixing device

ABSTRACT

Mixing devices for mixing fuel and air for a premix burner or furnace and furnaces (e.g., premix) with mixing devices. Furnaces may be for heating an occupied space, and may produce lower NOx emissions. A mixing device may be located within an inlet tube, may have a surface that is perpendicular to the direction of fuel flow or that forms a circle, or may have two surfaces held at substantially opposite angles to induce swirl. A portion of the mixing device may extend over an orifice of the fuel injector. A mixing device may be attached to the fuel injector, may be made from a piece of sheet metal, and may have a hole for attachment to the fuel injector. Mixing devices may have a center, two arms, and two ends, which may be separated by bends. A burner plate may be sandwiched between surfaces to allow for expansion.

RELATED PATENT APPLICATIONS

This patent application claims priority to U.S. patent application Ser.No. 12/793,318, filed on Jun. 3, 2010, titled PREMIX FURNACE AND METHODSOF MIXING AIR AND FUEL AND IMPROVING COMBUSTION STABILITY, naming fourof the same inventors and having the same assignee as listed above,which claims priority to Provisional Patent Application No. 61/183,934,filed on Jun. 3, 2009, titled LOW NOx FURNACE AND METHODS OF MAKING ANDCONTROLLING SAME, naming four of the same inventors that are listedabove. The contents of both of these priority patent applications areincorporated herein by reference. Certain terms, however, may be useddifferently in the Provisional Patent Application.

FIELD OF THE INVENTION

This invention relates to premix burners, furnaces, and methods ofmaking and improving such things. Particular embodiments concern fuelburner systems and furnaces that produce less NOx emissions thanalternative burners or furnaces.

BACKGROUND OF THE INVENTION

Various fuels have been burned for some time to produce heat for variouspurposes including heating spaces that people occupy, such as withinbuildings. Combustion of fuels has produced various pollutants that havebeen released into the atmosphere, and alterations have been made toequipment to reduce the quantity of certain pollutants that have beenemitted.

In various examples, natural gas and other fuels have been introducedinto heat exchanger tubes in furnaces and burned as the fuel mixes withair. Such processes, however, have resulted in the production of acertain amount of oxides of Nitrogen (NOx) during the combustionprocess. It has been known for some time that NOx production can bereduced significantly by mixing air and fuel in advance of combustionand then burning a controlled and substantially homogeneous mixture ofair and fuel. But premix burners have been plagued with noise resultingin oscillations of combustion and flow that have prevented premixburners from becoming workable in furnaces for occupied structures.

References that may provide useful background information include U.S.Pat. No. 5,971,745 (Bassett), U.S. Pat. No. 6,923,643 (Schultz), andU.S. Pat. No. 7,241,135 (Munsterhuis), as well as Demonstration oftricks and tools for solving self excited combustion oscillationproblems, by Peter K. Blaade (NOISE-CON 2008, Jul. 28-30, 2008), and Howto Solve Abnormal Combustion Noise Problems, by Peter K. Baade (SOUNDAND VIBRATION/JULY 2004).

Needs or potential for benefit or improvement exist for burners,furnaces, and methods of making and controlling such apparatuses thatreduce pollution (e.g., in comparison with alternative technologies),such as NOx emissions, from furnaces, for example, but that do notproduce unacceptable levels of noise. Needs and potential for benefit orimprovement also exist for burners, furnaces, and methods that do notrequire special installation procedures, that compensate for differentelevations, and that compensate for different heating characteristics ofthe fuel. Needs or potential for benefit or improvement also exist fordevices or apparatuses that produce less pollution than alternativeburners, such as NOx emissions, for example, that are suitable for usein furnaces, HVAC systems, or HVAC units, for example thatmore-effectively avoid producing pollution (e.g., NOx emissions) thatare inexpensive, that can be readily manufactured, that are easy toinstall, that are reliable, that have a long life, that are lightweight, that are efficient, that can withstand extreme environmentalconditions, or a combination thereof, as examples.

Needs or potential for benefit or improvement also exist for devices orapparatuses that reduce the production of pollution (e.g., in comparisonwith alternatives), such as NOx emissions, from furnaces, for example,that are quiet and that start reliably under a range of differentconditions. In addition, needs or potential for benefit or improvementexist for furnaces and HVAC units that include such devices orapparatuses that reduce pollution, as well as buildings having suchunits, systems, devices, or apparatuses.

Further, needs or potential for benefit or improvement exist for methodsof controlling, manufacturing, and distributing such furnaces, HVACunits, buildings, systems, devices, and apparatuses. Other needs orpotential for benefit or improvement may also be described herein orknown in the HVAC or pollution-control industries. Room for improvementexists over the prior art in these and other areas that may be apparentto a person of ordinary skill in the art having studied this document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view illustrating various components of a premixburner, for example, of a furnace for heating an occupied space;

FIG. 2 is a partial isometric view of an inlet end of an inlet tube thatforms an air inlet passage for a premix burner of a furnace, forexample, and also showing a fuel injector mounted in the inlet end and amixing device downstream of the fuel injector for swirling and mixingthe air and fuel prior to combustion;

FIG. 3 is a partial isometric view of an inlet end of an inlet tube thatforms an air inlet passage for a premix burner of a furnace, forexample, and also showing a fuel injector mounted in the inlet end, andshowing a different embodiment of a mixing device downstream of the fuelinjector for swirling and mixing the air and fuel prior to combustion,this mixing device being attached to the fuel injector;

FIG. 4 is a partial isometric view of an inlet end of an inlet tube thatforms an air inlet passage for a premix burner of a furnace, forexample, and also showing a fuel injector mounted in the inlet end, andshowing yet a different embodiment of a mixing device downstream of thefuel injector for mixing the air and fuel prior to combustion, thismixing device also being attached to the fuel injector;

FIG. 5 is a cross sectional side view (opposite side from FIG. 1) of theinlet tube and burner plate of FIG. 1 (and potentially of any of FIGS.2-4);

FIG. 6 is an isometric view of the inlet tube and burner plate of FIG.5, illustrating, among other things, the port pattern in the burnerplate;

FIG. 7 is an end view of the inlet tube and burner plate of FIGS. 5 and6;

FIG. 8 is a detail cross sectional side view (part of FIG. 5)illustrating the attachment of the burner plate to the air inletpassage;

FIG. 9 is an isometric view of a downstream flange that supports theburner plate;

FIG. 10 is a detail isometric view of the mixing device shown in FIG. 3;

FIG. 10 is a flat pattern of the mixing device of FIGS. 3 and 10;

FIG. 12 is a detail isometric view of the mixing device shown in FIG. 4;

FIG. 13 is a flat pattern of the mixing device of FIGS. 4 and 12;

FIG. 14 is an isometric view of an inlet tube (e.g., of FIG. 1),illustrating, among other things, a fluidic diode located within theinlet tube;

FIG. 15 is a detail cross-sectional side view of a combustion chamberand burner plate shown with a refractory material lining the combustionchamber;

FIG. 16 is a flow chart illustrating an example of a method of mixingair and fuel delivered to a premix burner (e.g., of a furnace); and

FIG. 17 is a flow chart illustrating an example of a method of improvingcombustion stability a premix burner (e.g., of a furnace).

These drawings illustrate, among other things, examples of certainaspects of particular embodiments of the invention. Other embodimentsmay differ. Various embodiments may include aspects shown in thedrawings, described in the specification, shown or described in otherdocuments that are incorporated by reference, known in the art, or acombination thereof, as examples.

SUMMARY OF PARTICULAR EMBODIMENTS OF THE INVENTION

This invention provides, among other things, mixing devices for mixingfuel and air, furnaces (e.g., for heating an occupied space), HVACunits, HVAC systems, methods, and buildings, many of which reduce NOxformation (e.g., in comparison with various alternatives), reduce noise,or both. Various embodiments provide, for example, as an object orbenefit, that they partially or fully address or satisfy one or more ofthe needs, potential areas for benefit, or opportunities for improvementdescribed herein, or known in the art, as examples. Certain embodimentsprovide, for example, devices or apparatuses that produce lesspollution, such as NOx emissions, from furnaces, for example, thatprovide an acceptable level of noise or that produce less noise, or acombination thereof, as examples.

In addition, particular embodiments provide, as objects or benefits, forinstance, furnaces, HVAC units, and methods (e.g., of controlling premixburners) that produce less pollution such as NOx emissions (e.g., incomparison with alternatives), that provide an acceptable level of noiseor that reduce noise (e.g., in comparison with alternatives), or acombination thereof, or buildings having such units, systems, devices,or apparatuses, as further examples. Further, some embodiments providemethods of manufacturing such furnaces, HVAC units, buildings, systems,devices, or apparatuses, as examples.

Specific embodiments of the invention provide various furnaces, forexample, for heating an occupied space. Such furnaces may produce lowerthan standard NOx emissions, for instance. In a number of embodimentssuch a furnace may include, for example, an air inlet passage, a fuelinjector, a mixing device, a burner plate, a combustion chamber, a heatexchanger, and a fan. The air inlet passage may include, for example, aninlet tube having an inlet end, and the fuel injector may be mounted atthe inlet end of the inlet tube. The fuel injector may include, forexample, an orifice for dispensing the fuel, and the fuel injector maybe oriented to dispense the fuel into the inlet end of the inlet tube.Space between the fuel injector and the inlet tube may permit air toenter the inlet tube around the fuel injector, for example.

In a number of embodiments, the mixing device may be downstream of thefuel injector, and the mixing device may mix the air and fuel prior tocombustion. In various embodiments, the mixing device is in addition tothe inlet tube. Further, the burner plate may be located downstream ofthe mixing device, and may separate unburned air and fuel mixture on anupstream side of the burner plate from burning air and fuel and productsof combustion on a downstream side of the burner plate. The burner platemay include, for example, multiple ports therethrough. The air and fuelmixture may pass through the ports in the burner plate. Still further,the combustion chamber may be located downstream of the burner plate,and may be defined on an upstream side by the burner plate.

Some embodiments include a heat exchanger, which may include multipleparallel heat exchanger tubes, that is downstream of the combustionchamber for transferring heat from the products of combustion, forexample, to air to be delivered to the occupied space. In addition, thefan may be located downstream of the heat exchanger, and may draw airthrough the air inlet passage, mixing device, burner plate andcombustion chamber. Further, in a number of embodiments, the fan maydraw products of combustion through the heat exchanger. Even further, incertain embodiments, the burner plate may be attached by beingsandwiched between opposing surfaces, for example, so that the burnerplate slides against the opposing surfaces when the burner plate expandsand contracts as the furnace cycles on and off.

In certain embodiments, the mixing device may be located inside the airinlet tube. The mixing device may include, for instance, a surface thatmay be substantially perpendicular to the direction of fuel flow exitingthe injector and that may be located in front of the orifice of the fuelinjector. In a number of embodiments, mixing device may include, forinstance, at least one flat metal plate that may be located downstreamof the orifice of the fuel injector. In particular embodiments, themixing device may include, for instance, two surfaces at the inlet endthat are held, for example, at substantially opposite angles so as toinduce swirl in the inlet tube. In some embodiments, the mixing devicemay include, for instance, two surfaces that are located downstream ofthe orifice of the fuel injector that are held at substantially oppositeangles inducing swirl in the fuel being dispensed from the orifice ofthe fuel injector and inducing swirl in the incoming air, whereby mixingof the two flows may be promoted.

Further, in various embodiments, the mixing device may be attached tothe fuel injector. In some embodiments, the mixing device may include,for instance, a piece of sheet metal that may have, for example,multiple bends. In particular embodiments, the piece of sheet metal mayinclude, for instance, a center and a hole, for example, that attachesthe piece of sheet metal to the fuel injector. In certain embodiments,the piece of sheet metal may include, for instance, two arms extendingfrom the center to two ends. In some embodiments, each arm may beseparated from the center by a first bend, and each end may be separatedfrom one of the arms by a second bend, for example.

In a number of embodiments, a fluidic diode may be located inside theinlet tube. The fluidic diode may be oriented to provide greaterrestriction to backflow than to forward flow, for example. In particularembodiments, the fluidic diode may include, for instance, a hollowfrustum. Further, in some embodiments, the fluidic diode may include afrustoconical portion that may include, for example, a larger circularopening and a smaller circular opening. The larger circular opening maybe closer to the fuel injector than the smaller circular opening, forexample. In certain embodiments, the fluidic diode may further include,for instance, a circular cylinder extending, for example, from thesmaller circular opening away from the fuel injector. In someembodiments, the circular cylinder may be substantially concentric withthe inlet tube, for example.

In some embodiments, the inlet tube may include, for instance, a bend.In particular embodiments such a bend may be (e.g., have an angle)between 22.5 and 135 degrees, for example. Further, in some embodiments,the combustion chamber may be lined with refractory insulation. Inparticular embodiments, however, the refractory insulation may beomitted from at least one portion of the combustion chamber thatincludes the ports. Even further, in some embodiments, the furnace mayinclude, for example, an adjustment input mechanism to adjust air/fuelratio or excess air, and a controller. The controller may include, forexample, a digital processor. In various embodiments, the controller mayreceive input from the adjustment input mechanism and may be in controlof (e.g., at least one of) the fuel injector, a fuel or gas regulator,an air damper, or the fan, as examples, and may control (e.g., at leastone of) a fuel delivery rate or an air flow rate through the air inletpassage, as examples. In a number of embodiments, the controller maycontrol combustion stoichiometry, for instance, using input from theadjustment input mechanism. In particular embodiments, for example, theadjustment input mechanism may receive an input of elevation, and thecontroller may use the input of elevation to adjust the air/fuel ratioor excess air, for example, to account for the elevation of theinstallation of the furnace. Further, in some embodiments, theadjustment input mechanism may be configured to receive an input of heatdelivery characteristics of the fuel gas, and the controller may beconfigured to use the input of heat delivery characteristics of the fuelgas to adjust the air/fuel ratio or excess air to account for the heatdelivery characteristics of the fuel gas delivered to the furnace.

Other specific embodiments include various mixing devices describedherein, for example, for mixing fuel and air, for instance, for afurnace, or in particular, for a premix furnace. Still other specificembodiments include various methods concerning premix burners or premixfurnaces. Examples include a number of methods of mixing air and fueldelivered to a premix burner, for example, of a furnace for heating anoccupied space. Such a method may include, for example, at least theacts of forming or obtaining a piece of sheet metal and attaching thepiece of sheet metal to a fuel injector of the premix burner. The pieceof sheet metal may have multiple bends, for example, and the act ofattaching the piece of sheet metal to the fuel injector of the premixburner may include attaching the piece of sheet metal so that at least aportion of the piece of sheet metal extends over the downstream side ofthe orifice of the fuel injector that dispenses the fuel. Other specificembodiments include various methods of improving combustion stability ina premix burner, for example, of a furnace for heating an occupiedspace. Such a method may include, for example, (e.g., in any order) atleast the acts of forming or obtaining a fluidic diode, and installingthe fluidic diode in an inlet tube of the premix burner. In a number ofembodiments, the fluidic diode may be installed in the inlet tubebetween a fuel injector and a combustion chamber. Further, in variousembodiments, the fluidic diode may be oriented to provide greaterrestriction to backflow than to forward flow.

In addition, various other embodiments of the invention are alsodescribed herein, and other benefits of certain embodiments may beapparent to a person of ordinary skill in the art.

DETAILED DESCRIPTION OF EXAMPLES OF EMBODIMENTS

A number of embodiments of the subject matter described herein includefurnaces, heating, ventilating, and air conditioning (HVAC) units, HVACsystems, devices for reducing pollution (e.g., in comparison withalternatives), NOx-reduction apparatuses, and methods of manufacturingfurnaces, HVAC units, HVAC systems, buildings, and devices for reducingpollution, NOx-reduction apparatuses, for example. As used herein “HVACunits” include air conditioning units, for example, direct expansionunits, which may be combined with gas furnaces, for instance. Variousembodiments include improvements that reduce pollution production (e.g.,over prior technology), such as NOx emissions, for instance. Variousembodiments of the subject matter described herein include a means forreducing pollution production or specifically a means for reducing NOxemissions, as examples. In addition, various embodiments include a meansfor mixing air and fuel for a premix burner, and means for improvingcombustion stability, for example, in a premix burner.

Certain embodiments of the subject matter described herein also includevarious procedures or methods of providing or obtaining differentcombinations of the components or structure described herein. Suchprocedures may include acts such as providing or obtaining variouscomponents described herein, and providing or obtaining components thatperform functions described herein, as well as packaging, advertising,and selling products described herein, for instance. Particularembodiments of the subject matter described herein also include variousmeans for accomplishing the various functions described herein orapparent from the structure described. Other embodiments may also beapparent to a person of ordinary skill in the art having studied thisdocument.

Various embodiments concern or involve premix burners. Very low NOxemission can be accomplished with certain premix burners. Although notall embodiments will provide such performance, at CO2 levels of about8.5%, for example, NOx emission can be in the area of 20-25 ppm air-free(about 10-12 ng/J, depending on furnace efficiency). Premix burners,however, may be sensitive to changes in fuel gas, ratio of methane toethane, WOBBE index of the fuel, altitude of installation, and the like.Lean mixtures may result in hard starts or stalls, as examples, and richmixtures may result in excessive noise or oscillation, as examples, orlack of combustion stability. As used herein “rich” does not necessarilymean richer than stoichiometric, but rather, means richer than optimal.In other words, “richer” may mean that there is less excess air. Inaddition, CO and NOx emissions may depend upon mixture. In a number ofembodiments, adjustments to the air/fuel mixture ratio may be made tocompensate for variations in these factors, (e.g., among other things).In different embodiments, open loop or closed loop (or feedback) controlsystems may be used. In some embodiments, adjustments may be mademanually, for instance, by the installer, by the owner, by an owner'srepresentative, or at the factory, to adjust for the location where afurnace or unit is or is to be installed, for example.

In some embodiments, on the other hand, one or more sensors may be usedto provide feedback to control mixture, for instance, automatically, asanother example. Various sensors may be used, in different embodiments,and sensors may be selected for longevity, accuracy, reliability, or acombination thereof, as examples. Some embodiments may combine manualinputs and automatic adjustments, as other examples. Automaticadjustments may be performed repeatedly, at regular intervals of time,or continuously, for example. Mixture may be controlled, in differentembodiments, by changing inducer fan (e.g., fan 17 described below)speed (e.g., using a variable-speed drive), by throttling air flow(e.g., with a damper), or by adjusting the rate of fuel delivery, asexamples. Sensors may sense flame condition, the products of combustion,or oscillations (e.g., noise, vibration, or pressure pulsations from theburner), as examples.

A number of embodiments are applied to a condensing furnace, forexample, rather than a non-condensing furnace. That does not mean thatall embodiments are limited to a condensing furnace, but there may beadvantage in condensing furnaces, for example, in the efficiency of thefurnace. In many embodiments, an inducer or fan draws combustionproducts through an air-heating exchanger (i.e., a heat exchanger, suchas heat exchanger 15, 16, or both, described in more detail below). Insome embodiments, the exchanger may be similar to hardware that is usedin other furnaces having conventional (non-premix) burners, for example.In certain embodiments, a premix burner may be applied to a smallcombustion chamber (e.g., 14 described below) at the inlet of the heatexchanger, for example. In some embodiments, the furnace utilizes a fuelor gas control and variable speed inducer. The gas control can beelectronically controlled, in a number of embodiments, to provide aspecified gas flow rate (e.g., by establishing the necessary gaspressure at a metering orifice). Likewise, the inducer speed can beelectronically controlled, in some embodiments, to provide requiredsystem flow, which may provide control of mixture, aeration, or excessair, for example.

In certain embodiments, a feature is to sense and control excess air sothat the combustion system can be operated effectively and reliablyunder differing conditions, for example. In various embodiments, varioussensing approaches may be used, such as differential flame rectificationfrom two flame sensors, low frequency visible light (red/yellow) signalfrom flame or glowing refractory material (e.g., utilizing cadmiumsulfide cell or similar), ultra violet light flame sensor, flameconductivity, inherent flame voltage, or a combination thereof, asexamples. Besides sensing of excess air, other control protocols ofvarying degrees of sophistication or of a more open-loop nature may beused, in some embodiments.

A number of embodiments of the subject matter herein are furnaces, forinstance, for heating an occupied space (e.g., while reducing NOxemissions in comparison with alternatives or keeping NOx emissionswithin acceptable levels). In various embodiments, such a furnace mayinclude, for example, an air inlet passage (e.g., 11 described below), afuel injector (e.g., 12 described below), and a mixing device (e.g., 21,31, or 41 described below) downstream of the air inlet passage anddownstream of the fuel injector for mixing the air and fuel prior tocombustion. Certain embodiments further include a burner plate (e.g., 13described below) downstream of the mixing device separating unburned airand fuel mixture on an upstream side of the burner plate from burningair and fuel and products of combustion on a downstream side of theburner plate. In a number of embodiments, the burner plate may be flat,while in other embodiments, the burner plate may be curved. In someembodiments, the burner plate may include, for example, multiple holes,orifices, or ports (e.g., 63 described below) therethrough for passageof the air and fuel mixture through the burner plate.

A number of embodiments further include a combustion chamber (e.g., 14described below) downstream of the burner plate, for example. In variousembodiments, the combustion chamber may have a particular volume. Anumber of embodiments further include multiple parallel heat exchangertubes (e.g., 15, 16, or both, described below) downstream of thecombustion chamber for transferring heat from the products of combustionto air (e.g., return air) to be delivered to the occupied space. Variousembodiments also include a fan (e.g., 17 described below) downstream ofthe heat exchanger tubes for drawing air (e.g., combustion air) throughthe air inlet passage, mixing device, and burner plate, and for drawingproducts of combustion through the heat exchanger tubes, for example.

Some embodiments further include a sensor (e.g., 133 described below)for detecting air/fuel ratio, excess air, or a condition of the burningair and fuel, as examples, and a controller (e.g., 195 described below)receiving input from the sensor and in control of at least one of thefuel injector, an air damper, or the fan, as examples, and controllingat least one of a fuel delivery rate or an air flow rate through the airinlet passage. In particular embodiments, the controller controlscombustion stoichiometry (e.g., excess air) using input from the sensor,for example. Other embodiments, however, may function satisfactorilywithout such a sensor, or even without such a controller.

In various embodiments, instead of a sensor, or in addition thereto, thefurnace may include an adjustment input mechanism (e.g., 190 describedbelow) for adjusting air/fuel ratio or excess air, as another example.In some such embodiments, the controller, which may be or include adigital processor, for example, may receive input from the adjustmentinput mechanism and may be in control of the fuel injector, a fuelregulator, an air damper, the fan, or a combination thereof, asexamples. In these embodiments, the controller may control the fueldelivery rate or the air flow rate through the air inlet passage, or maycontrol combustion stoichiometry using input from the adjustment inputmechanism, for example. A gas or fuel regulator may be a pressureregulator, for example, that may establish the pressure that motivatesflow through the fuel injector, for example. In other embodiments, afuel regulator may be a flow regulator, as another example.

In particular embodiments, the adjustment input mechanism may beconfigured to receive an input of elevation, for example, and thecontroller may be configured to use the input of elevation to adjust theair/fuel ratio or excess air to account for the elevation of theinstallation of the furnace, for instance. The controller may use theinput of elevation, for instance, to maintain substantially the sameair/fuel ratio at different elevations, for example, by adjusting theair flow rate or fuel flow rate. Further, in certain embodiments, theadjustment input mechanism may be configured to receive an input of heatdelivery characteristics of the fuel gas, as another example, and thecontroller may be configured to use the input of heat deliverycharacteristics of the fuel gas to adjust the air/fuel ratio or excessair to account for the heat delivery characteristics of the fuel gasdelivered to the furnace, for instance.

In various embodiments having a sensor, or otherwise, the mixing devicemay include, for example, a tube, for instance, having a round crosssection, having a substantially constant diameter, or both. Mixing in anentrance tube (e.g., before the burner plate) may be very effective, insome embodiments. In certain embodiments, the tube has a length and thelength is between five and twenty times the diameter, for instance.Further, in some embodiments, the tube may include, for example, a bend,for instance, between 22.5 and 135 degrees, and in some embodiments, thetube may have multiple bends. In various embodiments, the tube has onlyone bend or has only two bends, as examples. In different embodiments,the tube may include, for example, a bend between 60 and 120 degrees, abend between 75 and 105 degrees, a bend between 30 and 60 degrees, abend between 40 and 50 degrees, or a combination thereof, as examples.

Different size or capacity furnaces may be made, which may havedifferent size (e.g., cross-sectional area) tubes, such as mixing tubes,heat exchanger tubes, or the like. In some embodiments, different sizefurnaces may have tubes sized to have substantially equal velocities,for example, to assure adequate mixing (e.g., in mixing tubes) forsmaller units and yet to prevent excessive pressure drop in larger sizefurnaces. In particular embodiments, a single tube size may be used fordifferent size furnaces or burners, and inserts may be installed withinthe tubes for smaller size units to reduce the diameter orcross-sectional area and to increase the velocity. In certainembodiments, other mixing tube embodiments may be used that may havesimilar performance or function.

Further, some embodiments may include mixing devices, in addition to theinlet tube (e.g., inside the inlet tube). Various examples are describedherein and shown in the drawings. Such mixing devices may provide bettermixing, require shorter inlet tubes, allow for larger diameter inlettubes with less flow restriction, provide for less flow restrictionoverall, provide a more homogeneous mixture, provide more stablecombustion, prevent or reduce oscillations or noise, or a combinationthereof, as examples. In some embodiments, use of separate mixingdevices may reduce cost, reduce size, reduce weight, allow more inlettube design options, etc.

In a number of embodiments, the combustion chamber may be lined, forexample, with a refractory material such as a porous refractoryinsulation, which may dampen oscillation. In addition, a refractorymaterial lining the combustion chamber may reduce the temperature of thematerial (e.g., metal) forming the combustion chamber, which may promotematerial longevity, reduce oxidation, reduce thermal expansion (e.g.,and resulting stress and fatigue), and may also subject componentsoutside the combustion chamber to less heat.

In various embodiments, the combustion chamber may contain an igniter(e.g., 133 described below) for starting the furnace. The igniter may bea spark igniter, for example, and may ignite the flame with anelectrical spark, for instance. Or, in other embodiments, the ignitermay be a hot surface igniter, as another example. Furthermore, in someembodiments, the burner plate may have a plate cross-sectional area andthe combustion chamber may have a chamber cross-sectional area that issubstantially equal to the plate cross-sectional area. As used herein,“substantially equal to” means within plus or minus 10 percent.Moreover, in some embodiments, the burner plate has a platecross-sectional area that is rectangular, and in particular embodiments,the burner plate has a plate cross-sectional area that has rounded ends,rounded shoulders, or rounded corners, for instance.

Further, in certain embodiments, the combustion chamber may have achamber cross-sectional area that is rectangular, and in particularembodiments, the combustion chamber may have a chamber cross-sectionalarea that has rounded ends, rounded shoulders, or rounded corners, asexamples. In some embodiments, the combustion chamber may have a chambervolume that is greater than 100 cubic inches, a chamber volume that isless than 150 cubic inches, a chamber volume that is less than 125 cubicinches, or a combination thereof, as examples. In particularembodiments, for example, the burner may have a nominal full input rateof 72 kBtu/h, fired into four tubes. Furnaces with higher or lower inputmay have, in various embodiments, volume changes consistent with a widthchange of 2.5″ per tube or per 18 kBtu/h, as examples. The input perunit volume may stay about the same, in a number of embodiments,potentially with a slight deviation due to end effects, for instance.

In some embodiments, the combustion chamber may have a volume of about1.5 cubic inches per 1000 Btu/h of energy input rate or heat input rate,for example. Other furnaces, for comparison, range from about 2.4 to 7.2kBtu/h (e.g., for some low-emission premix pool heaters and otherresidential and light commercial boilers). As used herein, “about”, whenreferring to a quantity or dimension, means plus or minus 10 percent. Indifferent embodiments, the combustion chamber has a volume of about 1.0cubic inches per 1000 Btu/h, about 1.1 cubic inches per 1000 Btu/h,about 1.2 cubic inches per 1000 Btu/h, about 1.3 cubic inches per 1000Btu/h, about 1.4 cubic inches per 1000 Btu/h, about 1.5 cubic inches per1000 Btu/h, about 1.6 cubic inches per 1000 Btu/h, about 1.7 cubicinches per 1000 Btu/h, about 1.8 cubic inches per 1000 Btu/h, about 1.9cubic inches per 1000 Btu/h, or about 2.0 cubic inches per 1000 Btu/h,as examples. Other embodiments, however, may differ.

In some embodiments, the size, spacing, arrangement, or a combinationthereof, of the holes or ports through the burner plate may impactperformance. In addition, in a number of embodiments, burner sealingintegrity may be important. Burners that are not sealed well may operateerratically, generate higher NOx, or both, as examples. In certainembodiments, the ports through the burner plate may include, forexample, multiple first holes, for instance, having a first holediameter substantially equal to 1.25 mm, multiple second holes, forexample, having a second hole diameter substantially equal to 0.8 mm, orboth, and in some embodiments, the ports through the burner plate mayinclude, for example, multiple first holes that are each surrounded bymultiple second holes.

In some embodiments, the multiple second holes surrounding each of thefirst holes may all be substantially equal distant from the first holethat the second holes surround, for example, may all be located on acircle, or a combination thereof, as examples. In various embodiments,the circle may have a diameter that is substantially equal to 2.8 mm,3.2 mm, 3.5 mm, 3.8 mm, 4.2 mm, 4.5 mm, 5.0 mm, or 5.5 mm, as examples.In particular embodiments, the multiple second holes surrounding each ofthe first holes may all be substantially equal distant from adjacentsecond holes surrounding the same first hole, for instance.

In a number of embodiments, the multiple first holes may be arranged inmultiple shapes, each shape having between 25 and 250 first holes, eachshape having between 50 and 150 first holes, or each shape havingbetween 50 and 100 first holes, as examples. In particular embodiments,the shapes may be polygons, the shapes may have eight sides, the shapesmay be rectangles, the shapes may be squares, the shapes may havestraight sides, or a combination thereof, as examples. In someembodiments, the multiple first holes may be arranged in multiple shapesconnected by multiple carryover holes, but in other embodiments,carryover holes between the shapes may be lacking.

In certain embodiments, the multiple first holes may be substantiallyequally spaced from adjacent other first holes in the shape, themultiple first holes may be arranged in multiple substantially identicalshapes, or both, as examples. Moreover, in some embodiments, themultiple first holes may be arranged in four shapes, for example. Inother embodiments, on the other hand, the multiple first holes may bearranged in one, two, three, five, six, seven, eight, nine, or tenshapes, as other examples. Further, in various embodiments, the multiplefirst holes may be arranged in multiple lines, the multiple first holesmay be arranged in multiple columns, the multiple first holes may bearranged in multiple rows, or a combination thereof, as examples. Invarious embodiments, the number of holes may be related to the nominalinput rate (e.g., of 18 kBtu/h per heat exchanger tube, for instance, ofheat exchanger 15) and, in some embodiments, to the tube diameter, asexamples. In a particular embodiment, for example, 56 first holes ineach shape are arranged in a rectangle in seven rows and eight columns,and four such shapes are provided. (See, for example, FIGS. 6 and 7.)

In various embodiments that include a sensor, the sensor may be orinclude, for example, an oxygen sensor, a flame ionization sensor, adifferential flame rectification sensor, a chemiluminescence sensor, aradiant heat color sensor, a flame voltage sensor, a flame temperaturesensor, a microphone, a vibration sensor, a pressure sensor, anoscillation sensor, or a combination thereof, as examples. Further, incertain embodiments, the furnace may include, for example, a frequencyanalyzer, for instance, receiving input from the sensor, incommunication with the controller, or both.

As mentioned, a number of embodiments reduce noise produced by a premixburner or furnace. Certain things that have been found to be significantin quieting the burner or furnace in particular embodiments include: (1)increased pressure drop through the burner face, which may have anacoustic damping effect; (2) increased combustion chamber volume, whichmay cause less restriction of expansion, reduced pressure pulses, orboth; (3) increased surface and volume of refractory material due to thelarger chamber, which may result in improving acoustic damping; and (4)increased spacing of holes within the 7-hole set (e.g., six second holessurrounding a first hole), which may increase the ability of flameletsto accommodate pressure pulses without driving air/fuel mixture backthrough the ports, for example.

Other embodiments include various methods, for instance, of making apremix furnace for heating an occupied structure, for example, which mayinclude, for instance, a number of acts of obtaining or providing acombination of the components previously listed or described herein, asexamples. Other embodiments include various HVAC units, HVAC systems,and buildings that include, for example, a furnace described herein.Further embodiments include various methods of reducing noise from apremix burner that may include, for example, an act of increasingvelocity of an air and fuel mixture through holes or ports in a burnerplate. Moreover, various embodiments of methods of reducing noise from apremix burner may include, for example, an act of increasing combustionchamber volume, or both such acts. Furthermore, a number of embodimentsof methods may include, for example, acts of obtaining or providingvarious combinations of the components listed herein.

In a number of embodiments, premix burners may start better with aricher mixture than what is optimal for efficiency and low emissionsduring steady state operation, for example. Specific embodiments ofmethods of controlling a premix burner may include, for example (e.g.,in the following order) at least the acts of starting the burner with afirst air and fuel mixture ratio, igniting the burner, and changing theair and fuel mixture ratio as the burner warms up to a second air andfuel mixture ratio, for instance, wherein the first air and fuel mixtureratio has more fuel per unit of air than the second air and fuel mixtureratio.

In various embodiments, the air and fuel mixture ratio is controlled bychanging the rotational speed of a fan (e.g., inducer) used to movecombustion air through the burner, by modulating a fuel valve to adjusta rate of fuel delivery to the burner, by modulating a damper used tothrottle movement of combustion air through the burner, or a combinationthereof, as examples. In some embodiments, the act of changing the airand fuel mixture ratio as the burner warms up may include, for example,measuring time from the act of igniting the burner and changing the airand fuel mixture ratio as a function of that time.

Further, in some embodiments, the act of changing the air and fuelmixture ratio as the burner warms up may include, for example, measuringa temperature, for instance, with a temperature sensor, and changing theair and fuel mixture ratio as a function of that temperature, as anotherexample. In some embodiments, the temperature may be sensed at the inletof the inducer or fan during pre-purge, for example. The control mayadjust inducer speed (or fuel input), in some embodiments, to provide anair-fuel mixture ratio that provides more reliable ignition, forexample. An inducer speed change may essentially provide an adjustmentof air mass flow (e.g., made per the perfect gas law), for instance, toprovide a more-ideal air-fuel mixture. In particular embodiments,temperature may also (or instead) be measured (e.g., with a secondsensor) of the fuel gas at the injector orifice, for example, sincedensity also affects flow through an orifice.

Depending on the altitude of the installation, qualities of the fuel,and other variables, satisfactory settings for starting conditions mayvary, and some embodiments may provide for or compensate for suchconditions. In some embodiments, a method may include, for instance,after the act of igniting the burner, an act of detecting whether theburner has successfully ignited, and if the burner has not successfullyignited, repeating the act of igniting the burner at a different air andfuel mixture ratio. In a number of embodiments, such a process may berepeated at different mixtures (e.g., richer or leaner) until successfulignition occurs. Moreover, certain embodiments may include, for example,an act of remembering (e.g., automatically) a successful ignition airand fuel mixture ratio that was being provided when the burnersuccessfully ignited, and starting with that successful ignition air andfuel mixture ratio when the burner is ignited at a later time.

Furthermore, some embodiments may include, for example, an act ofremembering a successful ignition air and fuel mixture ratio that wasbeing provided when the burner successfully ignited, remembering atemperature condition when the burner successfully ignited, and startingwith that successful ignition air and fuel mixture ratio when the burneris ignited at a later time at the temperature condition. Certainembodiments may include, for example, an act of measuring thetemperature condition when the burner successfully ignited using atemperature sensor, and evaluating using the sensor whether thetemperature condition exists when the burner is ignited at a later time,for example. In some embodiments, the act of changing the air and fuelmixture ratio as the burner warms up may include, for example, graduallychanging the air and fuel mixture ratio over a period of time of atleast 5 seconds, gradually changing the air and fuel mixture ratio overa period of time of no more than 10 seconds, or both, as examples. Insome embodiments, however, the act of changing the air and fuel mixtureratio as the burner warms up may include, for example, graduallychanging the air and fuel mixture ratio over a period of time of atleast 10 seconds, as another example.

Certain embodiments may include indicator lights, error codes, recordsof attempts, or the like, which may be used by service personnel todiagnose problems if a furnace fails to start, for example, or otherwisefails to perform satisfactorily. Diagnostic information may help servicepersonnel to identify a source of the problem (e.g., a bad component,physical blockage, damage, or the like) or may help them to make manualadjustments that will provide better performance, as another example. Insome embodiments, diagnostic software may help to diagnose problems orobtain information on local conditions that may require compensatingadjustments in order to obtain desired performance. In some embodiments,units may be able to communicate with external networks regardingproblems or optimization of adjustments, as examples.

Some methods may include, for example, an act of measuring excess air inproducts of combustion and adjusting the air and fuel mixture ratio tocompensate for variations in heating value of the fuel, for example. Anumber of embodiments may compensate, not just for the heating value,but also for the density of the fuel, which may affect velocity of flowthrough the fuel injector orifice, for instance. Certain embodiments maycompensate for comprehensive or heat delivery characteristics of thefuel gas, for example. Accordingly, some methods may include, forexample, an act of measuring excess air in products of combustion andadjusting the air and fuel mixture ratio to compensate for heat deliverycharacteristics of the fuel gas, for example.

Moreover, some embodiments may include, for example, an act of measuringexcess air in products of combustion and adjusting the air and fuelmixture ratio to compensate for variations in elevation where the burneris located. Further, some embodiments may include, for example, an actof measuring at least one flame characteristic and adjusting the air andfuel mixture ratio to compensate for variations in heating value of thefuel to compensate for variations in elevation where the burner islocated, or both, as examples.

In addition, or instead, some embodiments may include, for example, anact of receiving a manually input adjustment and using the manuallyinput adjustment to adjust the air and fuel mixture ratio to compensatefor variations in heating value of the fuel (or heat deliverycharacteristics). Further, certain embodiments may include an act ofreceiving a manually input adjustment and using the manually inputadjustment to adjust the air and fuel mixture ratio to compensate forvariations in elevation where the burner is located, for example.Further, some methods may include, for example, an act of measuringconductivity of the products of combustion, an act of measuring voltageof the burner flame, an act of measuring burner noise and adjusting theair and fuel mixture ratio to control burner noise, an act of measuringburner vibration and adjusting the air and fuel mixture ratio to controlburner vibration, an act of measuring chemiluminescence, an act ofmeasuring UV, an act of red/yellow heat sensing, an act of measuringdifferential rectification, or a combination thereof, as examples.

Moreover, some embodiments may include an act of measuring NOx contentin the products of combustion and adjusting the air and fuel mixtureratio to control NOx production, an act of measuring CO content in theproducts of combustion and adjusting the air and fuel mixture ratio tocontrol CO production, an act of measuring oxygen content in theproducts of combustion and adjusting the air and fuel mixture ratio tocontrol oxygen content in the products of combustion, or a combinationthereof, as further examples. In other embodiments, other ways todetermine excess air may be used. In some embodiments, differentialrectification, radiant heat color, etc. may be used (e.g., instead or inaddition).

Some methods may include, for example, acts of forming, making,obtaining, or providing various combinations of the components listedabove or described herein, as examples. Other embodiments includevarious furnaces having a controller that is configured (e.g.,programmed or specifically made) to perform a method described herein,or wherein the controller includes, for example, software containinginstructions to perform a method described herein.

Some embodiments may recirculate some of the products of combustionthrough the burner to reduce oxygen availability to form NOx. Further,some embodiments may preheat combustion air (e.g., approaching or afterthe air inlet passage), fuel (e.g., approaching or after leaving thefuel injector),or both, for example, using heat from products ofcombustion after the products of combustion leave the heat exchangerthat transfers heat to the air that is to be delivered to the (e.g.,occupied) space. Such preheating may increase efficiency, for example.Further, some embodiments may have multiple combustion chambers (e.g.,one for each burner tube) or combustion may take place within the burnertubes, as other examples.

Other embodiments include a building that includes an HVAC unit, HVACsystem, air conditioning unit, furnace, or an apparatus or device (e.g.,for reducing NOx emissions) described herein, or an HVAC unit, HVACsystem, or air conditioning unit, having an apparatus described herein,as examples. Such a building may include walls and a roof, and may forman enclosure or enclose an occupied space, for example. A building orHVAC system may include, besides an HVAC unit, supply and return airductwork, registers, an air filter, a thermostat or controller, a loadcontroller, a condensation drain, or a combination thereof, for example.HVAC units may include a compressor, evaporator and condenser fans,motors for the compressor and fans, a housing, wiring, controls,refrigerant tubing, an expansion valve, and the like, for instance. Indifferent embodiments, HVAC units may be packaged units or may be splitsystems, as examples.

It should be noted that various methods in accordance with differentembodiments include acts of selecting, making, cutting, forming,bending, positioning, installing, or using certain components, asexamples. Other embodiments may include performing other of these actson the same or different components, or may include fabricating,assembling, obtaining, providing, ordering, receiving, shipping, orselling such components, or other components described herein or knownin the art, as other examples. Further, various embodiments of thesubject matter described herein include various combinations of thecomponents, features, and acts described herein or shown in thedrawings, for example.

Turning now to the specific examples of embodiments illustrated in thefigures, FIG. 1 illustrates an example of a premix furnace, furnace 10,for instance, for heating an occupied space. Furnace 10 may producelower than standard NOx emissions, for instance. As used herein,“standard” NOx emissions are emissions produced by typical priornon-premix furnaces. In embodiment illustrated, furnace 10 includes airinlet passage 11, fuel injector 12, a mixing device (e.g., 21, 31, or 41shown in FIGS. 2-4), burner plate 13, combustion chamber 14, heatexchanger tubes 15 and 16, and inducer or fan 17.

The embodiment show (e.g., in FIG. 1) includes multiple parallel heatexchanger tubes (e.g., 15 and 16) that are downstream of combustionchamber 14 for transferring heat from products of combustion, forexample, to air to be delivered to the occupied space. In addition, fan17 is located downstream of heat the exchanger tubes (e.g., 15 and 16),and draws air through air inlet passage 11, the mixing device (e.g., 21,31, or 41 shown in FIGS. 2-4), burner plate 13, and combustion chamber14. Further, fan 17 draws products of combustion through the heatexchanger tubes (e.g., 15 and 16).

Furnace 10 may include multiple heat exchanger tubes 15, only one ofwhich is visible in FIG. 1 because the other heat exchanger tubes 15 areparallel to, lined up with, and hidden behind the visible heat exchangertube 15. There may be, for example, multiple parallel heat exchangertubes (e.g., 15, 16, or both) that are downstream of combustion chamber14 for transferring heat from products of combustion, for example, toair to be delivered to the occupied space. There may be, for example,four heat exchanger tubes 15. Other embodiments may have 1, 2, 3, 5, 6,7, 8, 9, 10, 11, 12, 13, 14, or 15 heat exchanger tubes 15, as otherexamples. In the embodiment illustrated, each heat exchanger tube 15includes two 180 degree bends.

Although not shown in detail, heat exchanger tube 16 may further includemultiple (e.g., parallel) heat exchanger tubes. In a number ofembodiments, there may be more heat exchanger tubes 16 than heatexchanger tubes 15, but heat exchanger tubes 16 may be smaller indiameter. Heat exchanger tubes 16 may be housed within external fins,which may help to transfer heat from heat exchanger tubes 16 to the airthat is being delivered to the occupied space. The air to be deliveredto the occupied space may travel upward past heat exchanger tubes 16first, and then past heat exchanger tubes 15.

The air to be delivered to the occupied space may be moved by a bloweror indoor fan, which is not shown. The indoor fan may blow air past theheat exchanger tubes (e.g., 16 and 15) rather than drawing air past theheat exchanger tubes. Because the indoor fan blows air past the heatexchanger tubes (e.g., 16 and then 15), and the inducer or fan 17 forthe products of combustion draws air through the heat exchanger tubes(e.g., 15 and then 16) the indoor air usually has a greater pressurethan the products of combustion. As a result, if a breach or leakdevelops, for instance, in heat exchanger 15 or 16, the products ofcombustion do not leak into the air that is delivered to the occupiedspace.

In the embodiment shown, air inlet passage 11 includes, for example,inlet tube 18 having inlet end 19, and fuel injector 12 is mounted atinlet end 19 of inlet tube 18. As shown, for instance, in FIGS. 2-4,fuel injector 12 includes orifice 22 for dispensing fuel, and fuelinjector 12 is oriented to dispense fuel into inlet end 19 of inlet tube18. As shown, in this embodiment, fuel injector 12 is located partiallywithin inlet end 19 of inlet tube 18, and orifice 22 is located withininlet end 19 of inlet tube 18. Annular space 23 between fuel injector 12and inlet tube 18 (i.e., at inlet end 19) permits air to enter inlettube 18 around fuel injector 12.

In number of embodiments, the mixing device (e.g., 21, 31, or 41 shownin FIGS. 2-4) or target is downstream of fuel injector 12. The mixingdevice (e.g., 21, 31, or 41) may mix air and fuel (e.g., dispensed fromfuel injector 12) prior to combustion (e.g., in combustion chamber 14).In various embodiments, the mixing device (e.g., 21, 31, or 41 shown inFIGS. 2-4) or target may create turbulence which may promote mixing, mayblock or impede fuel from traveling downstream (e.g., within inlet tube18) without mixing with air, or both, as examples. The mixing device(e.g., 21, 31, or 41) may help to produce a more homogeneous mixture ofair and fuel before combustion in combustion chamber 14.

Further, burner plate 13 is located downstream of the mixing device(e.g., 21, 31, or 41), and, when furnace 10 is in operation, burnerplate 13 separates unburned air and fuel mixture on upstream side 131 ofburner plate 13 from burning air and fuel and products of combustion ondownstream side 132 of burner plate 13. FIGS. 5-8 and 15 illustrate,among other things, burner plate 13 in more detail. Burner plate 13includes, for example, multiple ports 63 therethrough. In the embodimentillustrated, air and fuel mixture pass through ports 63 in burner plate13. In the embodiment illustrated, cross over ports are not providedbetween the rectangular shapes (e.g., shown in FIGS. 6 and 7) formed byports 63. In other embodiments, however, cross over ports may beprovided between shapes to help the flame propagate between the shapes.

Still further, combustion chamber 14 is located downstream of burnerplate 13, and is defined on an upstream side by burner plate 13. Duringoperation of furnace 10, the air and fuel mixture ignites when it passesthrough ports 63 into combustion chamber 14. In normal operation offurnace 10, adequate velocity exists through ports 63 to prevent theconstant combustion within combustion chamber 14 from propagatingthrough ports 63 to ignite the air and fuel mixture within inlet tube18. As described above, in some embodiments, particular arrangement ofports 63 may be provided to obtain desired performance from furnace 10.

As shown in FIGS. 5 and 8, burner plate 13 is attached (e.g., to airinlet passage 11, or to a mixing chamber or burner body, for instance,at the end of inlet passage 11, or to combustion chamber 14) by beingsandwiched between opposing surfaces (e.g., of flanges 53 and 93), sothat burner plate 13 slides against the opposing surfaces when burnerplate 13 expands and contracts, for instance, due to temperature changesas furnace 10 cycles on and off. This way of mounting burner plate 13may reduce stress and fatigue of burner plate 13 as burner plate 13expands and contracts due to the heat of combustion and the cycling onand off of furnace 10. In some embodiments, close tolerances may beprovided around burner plate 13 to avoid air and fuel from leakingaround burner plate 13 into combustion chamber 14 without travelingthrough ports 63. In certain embodiments, a gasket may be used to avoidor reduce air and fuel from leaking around burner plate 13 intocombustion chamber 14 without traveling through ports 63. In someembodiments, however, a certain amount of such leakage may beacceptable.

Further, in the embodiment illustrated, burner plate 13 is curved.

Specifically, in the embodiment shown, upstream side 131 of burner plate13 is concave and downstream side 132 of burner plate 13 is convex. Thisshape may also reduce stress and fatigue, for example, resulting fromtemperatures changes and resulting expansion and contraction. In theembodiment illustrated, burner plate 13 is curved in two dimensions. Inother embodiments, the burner plate may be curved in just one dimension(e.g., in some embodiments the burner plate may include all or part of acircular cylinder).

As shown in FIGS. 2-4, in certain embodiments, the mixing device (e.g.,21, 31, or 41) is located inside air inlet tube 18 (e.g., within inletend 19). As shown in FIGS. 2 and 4, in some embodiments, the target ormixing device (e.g., 21 or 41) includes a (e.g., flat) surface (e.g., 24or 44) that is substantially perpendicular to the direction of fuel flowexiting fuel injector 12 and that is located in front of orifice 22 offuel injector 12. As used herein, “substantially perpendicular” meansperpendicular to within 10 degrees. Further, as used herein the“direction of fuel flow” is the average direction of fuel flow (e.g.,emerging from orifice 22). Even further, as used herein, “in front ofthe orifice” means that most of the fuel exiting the orifice impactswith or has its direction of flow substantially changed by the surface.

In the embodiment shown in FIGS. 4, 12, and 13, (e.g., flat) surface 44is made up of ends 128 and 129 that are attached to each other withdovetail joint 123. Ends 128 and 129 are each substantially asemicircle, in this embodiment (e.g., except for dovetail joint 123),which when attached, substantially form a circle that establishes flatsurface 44. Further, surface 44 is substantially a circle, in thisembodiment. In the embodiment shown in FIG. 2, (e.g., flat) surface 24is also substantially a circle. As used herein, “substantially a circle”means a circle except for attachment points, for example, referring tomixing device 41, except where bends 122 are formed or where arms 126and 127 attach. In various embodiments, the target or surface (e.g.,analogous to 24 or 44) may have a diameter that is between 0.5 inchesand 1.5 inches, between 0.75 and 1.0 inches, about 0.813 inches, orabout 20.6 mm, as examples. In other embodiments, the target or surface(e.g., analogous to 24 or 44) may have the shape of a polygon, square,rectangle, hexagon, or octagon, as other examples.

In number of embodiments, the mixing device (e.g., 21, 31, or 41 shownin FIGS. 2-4) includes, for instance, at least one (e.g., flat) metalplate (e.g., 25, 26, 35, 36, or 45) that is located downstream oforifice 22 of fuel injector 12. In particular embodiments, the mixingdevice (e.g., 31 shown in FIG. 3) includes, for instance, two surfaces(e.g., 27 and 28 shown in FIGS. 2 or 37 and 38 shown in FIG. 3), forinstance, at inlet end 19, that are held, for example, at substantiallyopposite angles (e.g., as shown) so as to induce swirl in inlet tube 18.As used herein, “substantially opposite angles”, at least in thiscontext, means that the angle between each of the two surfaces and thedirection of flow (e.g., the direction of fuel flow exiting fuelinjector 12) are equal, to within 10 degrees, but that these angles are180 degrees (plus or minus 10 degrees) apart from each other (around thedirection of flow, for example, the direction of fuel flow exiting fuelinjector 12).

In various embodiments, the angle between each of the two surfaces andthe direction of flow (e.g., the direction of fuel flow exiting fuelinjector 12) may be, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, or 80 degrees, or about such an angle, as examples. Asused herein, “about”, when referring to an angle, means plus or minus 5degrees. In a number of embodiments, the angle between each of the twosurfaces and the direction of flow (e.g., the direction of fuel flowexiting fuel injector 12) may be between 25 and 65 degrees between 30and 60 degrees, between 35 and 55 degrees, between 40 and 50 degrees, orabout 45 degrees, as examples.

In some embodiments, the mixing device (e.g., 21 or 31 shown in FIGS.2-3) includes, for instance, two surfaces (e.g., 27 and 28 shown inFIGS. 2 or 37 and 38 shown in FIG. 3) that are located downstream oforifice 22 of fuel injector 12 that are held at substantially oppositeangles (e.g., as shown) inducing swirl in fuel being dispensed fromorifice 22 of fuel injector 12 and inducing swirl in incoming air. In anumber of embodiments, such swirl promotes mixing of the two flows(e.g., of air and fuel). In different embodiments, these two surfacesmay be flat (e.g., 27 and 28 shown in FIGS. 2 or 37 and 38 shown in FIG.3), or may be curved, as examples. As used herein, flat, when referringto a surface or plane, means flat to within 10 percent of a length ofthe surface or plane.

Further, in various embodiments, the mixing device (e.g., 31 or 41 shownin FIGS. 3-4) is attached to fuel injector 12. As used herein, being“attached to” the fuel injector means that the mixing device is mountedon the fuel injector rather than being mounted on the inlet tube (e.g.,18, for example, as shown for mixing device 21 in FIG. 2). In someembodiments, there may be one or more other structural components,however, between the mixing device and the fuel injector. In variousembodiments, mounting the mixing device on the fuel injector (e.g.,mixing devices 31 or 41 shown in FIGS. 3-4, mounted to fuel injector 12)may provide for better or more consistent alignment between the mixingdevice and the orifice (e.g., 22) or fuel injector (e.g., 12).

In the embodiment illustrated, the mixing device (e.g., 21, 31, or 41shown in FIGS. 2-4) includes, or is made of, a piece of sheet metal.Some embodiments may be made from, for example, 18 gauge, 0.047-inch, or1.2 mm thick stainless steel (e.g., austenitic stainless steel). Otherembodiments may use 14, 16, 20, or 22 gauge stainless steel, as otherexamples. Other alternative materials include aluminized steel,galvanized steel, carbon steel, aluminum, copper, and nickel. Mixingdevice 31, introduced in FIG. 3, is shown in more detail in FIGS. 10-11and mixing device 41 introduced in FIG. 4 is shown in more detail inFIGS. 12-13. In the embodiments shown, these mixing devices (e.g., 31and 41) include multiple bends (e.g., 101 and 102 or 121 and 122 shownin FIGS. 10-13). In particular embodiments, the piece of sheet metal(e.g., mixing device 31 or 41) includes, for instance, a center (e.g.,105 or 125), which may have a hole (e.g., 100 or 120), for example, thatattaches, or may be used to attach, the piece of sheet metal (e.g.,mixing device 31 or 41) to fuel injector 12.

Hole 100 or 120 may have a diameter of about 0.384 inches, about 9.8 mm,about 0.405 inches, or about 10.3 mm, as examples. Further, in variousembodiments, surface 24 or 44 may be ¼ to 2 inches from fuel injector 12or from orifice 22. In particular embodiments, for example, surface 24or 44 may be ½ to 1 inches from fuel injector 12 or from orifice 22. Incertain embodiments, for example, surface 24 or 44 may be about 0.265inches or 6.7 mm from fuel injector 12 or from orifice 22.

In the embodiments shown in FIGS. 3, 4, and 10-13, the piece of sheetmetal (e.g., mixing device 31 or 41) includes, for instance, two arms(e.g., 106 and 107 or 126 and 127 shown in FIGS. 10-13) extending fromthe center (e.g., 105 or 125) to two ends (e.g., 108 and 109 or 128 and129), for example, each located in front of orifice 22 of fuel injector12 (e.g., as shown in FIGS. 3 and 4). In a number of embodiments, eacharm (e.g., 106 and 107 or 126 and 127) may have a width of about 0.25inches or about 6.4 mm, for example. In these embodiments, each arm(e.g., 106 and 107 or 126 and 127 shown in FIGS. 10-13) is separatedfrom the center (e.g., 105 or 125) by a first bend (e.g., 101 or 121),and each end (e.g., 108 and 109 or 128 and 129) is separated from one ofarms (e.g., 106 and 107 or 126 and 127) by a second bend (e.g., 102 or122), for example.

In the embodiments shown, bends 101 have an angle of about 90 degrees,and bends 121 have an angle (from straight) of about 74 degrees. Otherembodiments may have an analogous angle (from straight) of about 45, 50,55, 60, 65, 70, 75, 80, 85, or 95 degrees, as other examples. Inaddition, in the embodiments shown, bends 102 have an angle of about 50degrees, and bends 122 have an angle (from straight) of about 107degrees. Other embodiments may have an analogous angle (from straight)of about 20, 25, 30, 35, 40, 45, 55, 60, 65, 70, 75, 80, 85, 95, 100,105, 106, 110, 115, 120, 125, 130, 135, 140, or 150 degrees, as otherexamples.

Once installed on fuel injector 12, in some embodiments, these mixingdevices (e.g., 31) may not extend outside of a particular circlediameter. Otherwise the mixing device cannot be inserted into mount 32within burner tube 18 with the mixing device attached to the fuelinjector. In the embodiment illustrated, this particular circle diameteris 0.600 inches, or 15.2 mm, for example. Mixing device 41, however, hasa larger diameter, and mixing device 41 may be attached to fuel injector12 after fuel injector 12 is attached to mount 32 of inlet tube 18.Other embodiments may have a different type of mount between the fuelinjector and inlet tube that may permit a mixing device of the size ofmixing device 41 to be attached to the fuel injector first beforeinstalling the fuel injector.

FIG. 14 illustrates that, in number of embodiments, a fluidic diode(e.g., fluidic diode 140) may be located inside inlet tube 18. As usedherein, a “fluidic diode” is device that, without moving parts, at leastat a particular flow rate, provides more pressure drop for flow in onedirection than in an opposite direction. In the embodiment illustrated,fluidic diode 140 is oriented to provide greater restriction to backflowthan to forward flow, for example. (As used herein, “forward flow” isflow from fuel injector 12 to combustion chamber 14.) In the embodimentshown, fluidic diode 140 includes, for instance, hollow frustum orfrustoconical portion 141. In various embodiments, hollow frustum orfrustoconical portion 141 may have walls 145 at an angle of about 30degrees from the centerline of inlet tube 18. In other embodiments,hollow frustum or frustoconical portion 141 may have walls 145 at anangle of about 15, 20, 25, 35, 40, 45, or 50 degrees from the centerlineof inlet tube 18, as other examples.

In the embodiment depicted, hollow frustum or frustoconical portion 141includes, for example, larger opening 143 and smaller opening 144. Inthe embodiment shown, larger opening 143 and smaller opening 144 areboth circular. In some embodiments, larger (e.g., circular) opening 143may have a diameter of about 2 9/64 inches (OD) and smaller (e.g.,circular) opening 144 may have a diameter of about 1 13/64 inches orabout 29/32 inches (ID) as examples. As illustrated, in this particularembodiment, larger opening 143 is closer to fuel injector 12 thansmaller opening 144.

In the embodiment shown, fluidic diode 140 further includes, forinstance, (e.g., circular) cylinder 142 extending, for example, fromsmaller opening 144 away from fuel injector 12. In the embodiment shown,cylinder 142 is attached to smaller opening 144. In some embodiments,cylinder 142 may have a diameter of about 1 13/64 inches or about 29/32inches (ID), as examples, and may be about 3 inches long. In otherembodiments, cylinder 142 may be about 1, 1.5, 2, 2.5, 2.75, 3.25, 3.5,4, 4.5, 5, or 6 inches long, as other examples In the embodimentillustrated, cylinder 142 is substantially concentric with inlet tube18, for example. Other embodiments may lack a cylinder, or may include acylinder that is not concentric. Other embodiments may have a crosssection or openings other than circular, such as polygonal, square,rectangular, triangular, pentagonal, hexagonal, octagonal, or oval, asexamples.

In a number of embodiments, a burner or furnace may include a separatemixing device (e.g., 21, 31, or 41) and fluidic diode (e.g., 140). Afluidic diode, however, may promote mixing by itself. In fact, in someembodiments, a fluidic diode may be used that may produce sufficientmixing that a separate mixing device is not needed. An example is ahollow cone mounted within the inlet tube (e.g., 18) downstream of thefuel injector (e.g., 12) with the point of the cone in front of theorifice (e.g., 22) of the fuel injector and the open base of the conepointed downstream or toward the burner plate (e.g., 13). In variousembodiments, such a cone may be concentric or substantially concentricwith the inlet tube, for instance. In some embodiments, vanes may extendfrom the cone to the inside of the inlet tube. The vanes may be angled,in some embodiments, to produce swirl in the inlet tube downstream ofthe cone, for example, to promote mixing of the air and fuel.

In other embodiments, a cup or hollow pyramid with an open base may beused instead of a cone, with the point of the pyramid or convex surfaceof the cup facing upstream toward the orifice of the fuel injector andthe open base of the pyramid or concave surface of the cup facingdownstream. Such a pyramid may have 3, 4, 5, 6, 7, or 8 sides, asexamples, may have a polygonal cross section, or both, for instance.Such a cup may be part of a hollow sphere, such as a hollow hemisphere,or may be a hollow parabola, as examples. In various embodiments,however, the mixing device may provide the most benefit close to thefuel injector, while the fluidic diode may provide more benefit closerto the burner plate. Further, in some embodiments, the mixing device maybe a fluidic diode, and another fluidic diode may be provided furtherdownstream. In some such embodiments, both such fluidic diodes may beoriented to provide greater restriction to backflow than to forwardflow.

As shown in FIGS. 1, 5, 6, and 14, inlet tube 18, in the embodimentillustrated, includes bend 58. In various embodiments such a bend (e.g.,58) may have an angle between 22.5 and 135 degrees, for example. Otherexamples of angles are identified herein. In the embodiment illustrated,bend 58 has an angle of about 90 degrees, for example. Other embodimentsmay not have a bend, or may have more than one bend. One or more bends(e.g., 58) may help to promote mixing of the air and fuel, may impactoscillations or noise, or a combination thereof.

As shown in FIG. 15, in some embodiments, combustion chamber 14 is linedwith refractory insulation 150. In particular embodiments, however, suchas in the embodiment shown, refractory insulation 150 may be omittedfrom at least one portion of the combustion chamber 14 (e.g., thatincludes ports 63). Refractory material or insulation 150 may keep theoutside of combustion chamber 14 cooler, which may reduce stress andfatigue or may keep neighboring components cooler. In some embodiments,refractory insulation 150 may also help to dampen oscillations or noise.

In some embodiments, a refractory shield may be formed over theun-ported surfaces of the burner plate (e.g., 13), which may be donespecifically to reduce the temperature of the burner plate and thusreduce oxidation and stress of the burner plate. This may provide asuccessful perforated steel burner in a radiant refractory combustionchamber (e.g., 14). Certain embodiments include (e.g., in combinationwith the refractory insulation 150 shown), a port field arrangement thatoffers greater shielding. For example, in some embodiments, port groups(e.g., the rectangular shapes of ports 63 shown) may be arranged incontinuous side-to-side rows, leaving adjacent bare surfaces that may bemore-effectively shielded (e.g., with refractory insulation such as150).

FIG. 15 also illustrates igniter or sensor 133 within combustion chamber14. Various examples of igniters and sensors are described herein, forexample.

As shown in schematic form in FIG. 1, in some embodiments, furnace 10includes, for example, adjustment input mechanism 190, for instance, toadjust air/fuel ratio or excess air. Furnace 10 also includes, in theembodiment illustrated, controller 195. Controller 195 includes, in thisembodiment, digital processor 196. In various embodiments, controller195 may receive input from adjustment input mechanism 190 and may be incontrol of (e.g., at least one of) fuel injector 12, a gas regulator, anair damper, or fan 17, as examples, and may control (e.g., at least oneof) fuel delivery rate or air flow rate (e.g., through air inlet passage11), as examples. In a number of embodiments, controller 195 may controlcombustion stoichiometry, for instance, using input from adjustmentinput mechanism 190.

In particular embodiments, for example, adjustment input mechanism 190may be or include a user interface, such as a keypad, touch screen, setof switches (e.g., dip switches), knob, or a combination thereof. Incertain embodiments, for example, adjustment input mechanism 190 mayinclude a screen or display. Further, in some embodiments, adjustmentinput mechanism 190 may be a plug or receptacle and a user, installer,or service person may plug in a device such as a computer, diagnostictool, control mechanism, or the like.

In particular embodiments, for example, adjustment input mechanism 190may receive input of elevation, and controller 195 may use the input ofelevation to adjust the air/fuel ratio or excess air, for example, toaccount for elevation of installation of furnace 10. for instance, inputmechanism 190 may receive input of elevation from an installer, a user,a distributer, or from the manufacturer, as examples. Further, in someembodiments, adjustment input mechanism 190 may be configured (e.g.,programmed) to receive input of heat delivery characteristics of thefuel gas, for instance, and controller 195 may be configured (e.g.,programmed) to use the input of heat delivery characteristics of thefuel gas to adjust the air/fuel ratio or excess air, for instance, toaccount for heat delivery characteristics of the fuel gas delivered tofurnace 10.

Other specific embodiments include various methods concerning premixburners or premix furnaces (e.g., furnace 10 shown in FIG. 1). Examplesinclude a number of methods of mixing air and fuel delivered to a premixburner, for example, of furnace 10 for heating an occupied space. FIG.16 illustrates an example of such a method, method 160, that includes,for example, at least act 161 of forming or obtaining a target, and act162 of attaching the target to a fuel injector. For instance, act 161 offorming or obtaining a target may include forming or obtaining a mixingdevice (e.g., 31 or 41), which may be or include a piece of sheet metal.Further, act 162 of attaching the target may include attaching themixing device (e.g., 31 or 41) or piece of sheet metal, for instance,specifically to fuel injector 12 of the premix burner (e.g., of furnace10). In act 162, the mixing device (e.g., 31 or 41) or piece of sheetmetal may have multiple bends (e.g., 101 and 102 or 121 and 122), forexample, or the act of forming the piece of sheet metal may specificallyinclude bending the sheet metal. Further, in a number of embodiments,act 162 of attaching the mixing device or piece of sheet metal (e.g., 31or 41) to the fuel injector (e.g., 12) of the premix burner (e.g., offurnace 10) includes attaching the piece of sheet metal so that at leastportion of piece of sheet metal (e.g., end 108, 109, 128, 129, or acombination thereof) extends over the downstream side of the orifice(e.g., 22) of the fuel injector (e.g., 12) that dispenses fuel.

Moreover, other embodiments include various methods of improvingcombustion stability in a premix burner, for example, of a furnace(e.g., 10) for heating occupied space. For instance, FIG. 17 illustratesmethod 170 that includes, for example, at least act 171 of forming orobtaining a fluidic diode (e.g., 140 shown in FIG. 14), and act 172 ofinstalling the fluidic diode, for example, in inlet tube 18 of thepremix burner (e.g., furnace 10). Fluidic diode 140 may be installed ininlet tube 18 between fuel injector 12 and combustion chamber 14, forexample (e.g., between inlet end 19 and burner plate 13). Further, invarious embodiments, the fluidic diode (e.g., 140) may be oriented, forexample, to provide greater restriction to backflow than to forward flow(e.g., as shown).

Various embodiments of the subject matter described herein includevarious combinations of the acts, structure, components, and featuresdescribed herein, shown in the drawings, or known in the art. Moreover,certain procedures may include acts such as obtaining or providingvarious structural components described herein, obtaining or providingcomponents that perform functions described herein. Furthermore, variousembodiments include advertising and selling products that performfunctions described herein, that contain structure described herein, orthat include instructions to perform functions described herein, asexamples. Such products may be obtained or provided throughdistributors, dealers, or over the Internet, for instance. The subjectmatter described herein also includes various means for accomplishingthe various functions or acts described herein or apparent from thestructure and acts described.

1. A furnace for heating an occupied space, the furnace comprising: anair inlet passage comprising an inlet tube having an inlet end; a fuelinjector mounted at the inlet end of the inlet tube, the fuel injectorcomprising an orifice that dispenses the fuel, wherein the fuel injectoris oriented so that the fuel injector dispenses the fuel into the inletend of the inlet tube, and wherein space between the fuel injector andthe inlet tube permits air to enter the inlet tube around the fuelinjector; a mixing device downstream of the fuel injector that mixes theair and fuel prior to combustion, wherein the mixing device is inaddition to the inlet tube and the mixing device is located inside theinlet tube; a burner plate downstream of the mixing device separatingunburned air and fuel mixture on an upstream side of the burner platefrom burning air and fuel and products of combustion on a downstreamside of the burner plate, the burner plate comprising multiple portstherethrough that the air and fuel mixture pass through; a combustionchamber downstream of the burner plate and defined on an upstream sideby the burner plate; a heat exchanger downstream of the combustionchamber that transfers heat from the products of combustion to air to bedelivered to the occupied space; and a fan downstream of the heatexchanger that draws air through the air inlet passage, mixing device,burner plate and combustion chamber, and that draws products ofcombustion through the heat exchanger.
 2. The furnace of claim 1 whereinthe mixing device comprises a surface that is substantiallyperpendicular to the direction of fuel flow exiting the injector andthat is located in front of the orifice of the fuel injector.
 3. Thefurnace of claim 2 wherein the surface of the mixing devicesubstantially forms a circle.
 4. The furnace of claim 1 wherein themixing device comprises multiple surfaces that are held at angles so asto induce swirl in the inlet tube.
 5. The furnace of claim 1 wherein themixing device comprises multiple surfaces that are located downstream ofthe orifice of the fuel injector that are held at angles inducing swirlin the fuel being dispensed from the orifice of the fuel injector andinducing swirl in the air, whereby mixing of the fuel and the air ispromoted.
 6. The furnace of claim 1 wherein the mixing device comprisesa piece of sheet metal comprising multiple bends.
 7. The furnace ofclaim 1 wherein the mixing device comprises a hole that attaches themixing device to the fuel injector.
 8. The furnace of claim 1 whereinthe mixing device comprises a center and two arms extending from thecenter to two ends, wherein each arm is separated from the center by afirst bend, and wherein each end is separated from one of the arms by asecond bend.
 9. The furnace of claim 1 wherein the burner plate isattached by being sandwiched between opposing surfaces so that theburner plate slides against the opposing surfaces when the burner plateexpands and contracts as the furnace cycles on and off.
 10. The furnaceof claim 1 wherein the mixing device comprises: a center; a first end; asecond end; a first arm extending from the center to the first end, thefirst arm having a first arm length extending from the center to thefirst end; a second arm extending from the center to the second end, thesecond arm having a second arm length extending from the center to thesecond end; a first bend between the center and the first arm; a secondbend between the center and the second arm; a third bend between thefirst arm and the first end; and a fourth bend between the second armand the second end; wherein: the center, the first end, the second end,the first arm, and the second arm all have a common thickness; thecenter has a center width that is perpendicular to the first arm length,to the second arm length, and to the thickness of the center; the firstend has a first end width that is perpendicular to the first arm lengthand to the thickness of the first end; the second end has a second endwidth that is perpendicular to the second arm length and to thethickness of the second end; the first arm has a first arm width that isperpendicular to the first arm length and to the thickness of the firstarm; the second arm has a second arm width that is perpendicular to thesecond arm length and to the thickness of the second arm; the centerwidth is greater than the first arm width; the center width is greaterthan the second arm width; the first end width is greater than the firstarm width; and the second end width is greater than the second armwidth.
 11. A mixing device for mixing fuel and air for a premix burner,the mixing device comprising: a center; a first end; a second end; afirst arm extending from the center to the first end, the first armhaving a first arm length extending from the center to the first end; asecond arm extending from the center to the second end, the second armhaving a second arm length extending from the center to the second end;a first bend between the center and the first arm; a second bend betweenthe center and the second arm; a third bend between the first arm andthe first end; and a fourth bend between the second arm and the secondend; wherein: the center, the first end, the second end, the first arm,and the second arm all have a common thickness; the center has a centerwidth that is perpendicular to the first arm length, to the second armlength, and to the thickness of the center; the first end has a firstend width that is perpendicular to the first arm length and to thethickness of the first end; the second end has a second end width thatis perpendicular to the second arm length and to the thickness of thesecond end; the first arm has a first arm width that is perpendicular tothe first arm length and to the thickness of the first arm; the secondarm has a second arm width that is perpendicular to the second armlength and to the thickness of the second arm; the center width isgreater than the first arm width; the center width is greater than thesecond arm width; the first end width is greater than the first armwidth; and the second end width is greater than the second arm width.12. The mixing device of claim 11 wherein the first bend plus the secondbend equals 180 degrees and the third bend plus the fourth bend equals180 degrees.
 13. The mixing device of claim 11 wherein the first armlength is greater than the first arm width and the second arm length isgreater than the second arm length.
 14. The mixing device of claim 13further comprising a hole through the thickness and wherein the mixingdevice is made of sheet metal, the first bend plus the second bendequals 180 degrees, and the third bend plus the fourth bend equals 180degrees.
 15. A mixing device for mixing fuel and air in a premixfurnace, the mixing device comprising first portion comprising a holethrough the first portion of the mixing device that attaches the mixingdevice to a fuel injector; and a second portion of the mixing device,which, when the mixing device is attached to the fuel injector, extendsover an orifice of the fuel injector.
 16. The mixing device of claim 15further comprising at least one arm that extends from the first portionto the second portion.
 17. The mixing device of claim 16 furthercomprising a first bend between the at least one arm and the firstportion and a second bend between the at least one arm and the secondportion.
 18. The mixing device of claim 17 wherein the first bend plusthe second bend equals 180 degrees.
 19. The mixing device of claim 17wherein the least one arm comprises a first arm and a second arm thateach extend from the first portion to the second portion.
 20. The mixingdevice of claim 15 wherein the mixing device is made of sheet metal.